For this compound a remarkably large coupling \(\lambda \)\(\approx \) 4.5 was reported, reproducing reasonably well results of Peng et al.[1]} This value is perhaps the largest value from DFT-ME theory for a real (if still only predicted) compound.
This large value of \(\lambda \)  `benefits' from very soft phonons, that is, being very close to a dynamical instability, which is a typical occurrence in several crystal classes.[2]}
When this occurs, corrections for anharmonicity, quantum fluctuations of H, and nonlinear EP coupling become necessary to pin down the critical pressure for instability as well as for the most complete prediction of T\(_c\) . Generally but especially in hydrides, low frequency modes do not promote T\(_c\)  as much as their contribution to \(\lambda \)  would suggest[2]}, [4]} (see Sec. VI.B).
